A recent wireless communication system employs a variable modulation scheme in which the transmission capacity is expanded by increasing a modulation level when fading in a transmission channel is not severe and the transmission capacity is reduced by decreasing a modulation level when fading is severe.
Diversity communication is generally thought to be essential in a case of a multipath-fading channel. In particular, quadruple-diversity reception is generally thought to be necessary in a case of the tropospheric scatter propagation.
FIG. 7 is a block diagram illustrating a configuration of a common wireless communication device performing diversity reception. Referring to FIG. 7, the wireless communication device includes four systems of matching filters 601, a combiner 602, a feedforward filter 603, a combiner 604, a demodulator 605, a feedback filter 606, and a subtractor 607.
The wireless communication device illustrated in FIG. 7 performs quadruple-diversity reception by maximum ratio combining using the matching filters 601. Specifically, received signals 1 to 4 are passed through the four systems of the matching filters 601. The matching filters 601 gather time-dispersed multipath signals at a reference timing, and using the signals as received signals maximizes a signal-to-noise ratio (SNR). The combiner 602 combines the outputs of the matching filters of the respective systems. Thus, the maximum ratio combining in the quadruple diversity is performed. A decision feedback equalizer composed of the feedforward filter 603 and the feedback filter 606 eliminates intersymbol interference.
As a related art, PTL 1 describes a diversity reception device that can reduce the effects of the fading and a multipath generated in a channel.